This study presents an analysis of air and water movement in a sand column, which takes air compressibility into account. The influence of air on water intake is assessed when water content is imposed at the soil surface. When air can move freely ahead of the wetting front, we found that air compressibility is negligible, but that air movement increases water intake by a small percentage. When air must escape through the sand surface air compressibility increases water intake by a small percentage, although the overall effect of air movement is to reduce water flow. The results of the theory are illustrated and confirmed from previous experimental observations.